title: Regioselective N-acetylation as a route of nitro-9-phenylenediamine metabolism by rat liver cytosol.
abstract: Regioselectivity in N-acetylation of nitro-0-phenylenediamine, a widely used hair dye component, by rat liver cytosolic N-acetyltransferases was studied in relation to its substituent effects on enzymatic N-acetylation of mono-substituted anilines. Nitro-p-phenylenediamine was acetylated specifically at the N4-position to afford the N4-monoacetate, a major urinary metabolite in the rat, when incubated with rat liver cytosol fortified with acetyl-coenzyme A. N1-Acetylation of nitro-p-phenylenediamine did not take place even when the N4-monoacetate was used as a substrate, suggesting a strong steric hindrance effect of the ortho nitro group on the enzymatic N1-acetylation. The steric hindrance effect of the nitro group on the cytosolic N-acetylation of the ortho amino group was revealed by a comparative study carried out by using aniline, three respective regioisomers of nitroanilines and phenylenediamines as model substrates. The comparative study also indicated the enzymatic N-acetylation of the mono-substituted anilines to be strongly influenced by the electronic effect of the substituents. Regioselective N-acetylation in the hepatic cytosol was also investigated with N1- and N4-monoacetates of 1,2,4-triaminobenzene. The monoacetates yielded the N1,N4-diacetate, another major urinary metabolite of the hair dye component, in the rat, without concomitant formation of the N2,N4-diacetate or the N1,N2,N4-triacetate. The triacetate was formed only from the N1,N2-diacetate in the enzymatic reactions. A comparative study, carried out by using N-mono-acetates of three regioisomeric phenylenediamines, indicated that the N-acetyl group had a potent steric hindrance effect on the primary amino group at the ortho position.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Hatano Research Institute, Food and Drug Safety Center, Kanagawa, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Nakao
authors.forename: Y
authors.initials: Y
authors.lastname: Goto
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuki
authors.forename: A
authors.initials: A
authors.lastname: Hiratsuka
authors.forename: T
authors.initials: T
authors.lastname: Watabe
mesh_terms: D000107:Acetylation; D000818:Animals; D002273:Carcinogens / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008968:Molecular Conformation; D010655:Phenylenediamines / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D002273:Carcinogens; D010655:Phenylenediamines; C014706:2-nitro-4-phenylenediamine